Radio systems are systems that transmit and receive signals in the form of electromagnetic waves in the RF range of approximately 3 kiloHertz (kHz) to 300 gigaHertz (GHz). Radio systems are commonly used for wireless communications. Two radio units in the same radio system can exchange information wirelessly using protocols such as Bluetooth™, wireless local area network (WLAN) or IEEE 802.15.4 compliant protocols. Some examples of such radio systems include wireless sensor network, Bluetooth enabled handsets, and smart home systems.
In some settings, it may be desirable to be able to determine distance between two radio units automatically (i.e. without or with minimal user intervention), a process referred to as “RF ranging.” For example, pair-wise range measurements between a mobile device and multiple access points with RF ranging can identify the location of the mobile device.
One approach to determining distance between two radio units is to employ phase based measurements, where the differences in phase between signals are analyzed to estimate distance. In such measurements, reference clock signals of the different radio units need to be synchronized to be within tight timing tolerances as specified by a particular application. Such synchronicity may be very difficult to achieve, especially at high clock speeds.